1. Field of the Invention
The present invention relates to an information processing apparatus and a loop antenna and, in particular, an information processing apparatus and loop antenna, which allow the communication, transmission or receipt with the other party by radio.
2. Description of the Related Art
In the recent years, a non-contact IC (Integrated Circuit) card has been widely spread. An IC card can record a larger amount of data than that of the other cards such as a magnetic card and can encrypt data, resulting in a high level of security. For example, an IC card may be applied as a storage card for electronic money, a commuter ticket in a transport facility and a credit card in a financial facility. Contact and non-contact type IC cards are available depending on the communication method. The non-contact type IC card internally contains a loop antenna having an antenna line wired by a predetermined number of turns to be used for communication with a terminal such as a special reader/writer by weak radio.
A non-contact type IC card may be built in mobile equipment such as a cellular phone so as to include not only an IC card function being capable of communicating with a special reader/writer but also a reader/writer function (R/W function) being capable of communicating with other non-contact type IC cards. In the following description, the term, card mode, refers to that a non-contact type IC card operates with the IC card function, and the term, reader/writer mode, refers to that a non-contact IC card operates with the reader/writer function.
A front end circuit 1 of a non-contact type IC card in the past, which operates in the card mode, includes a capacitor C1, a loop antenna 2 and a transmitting/receiving circuit 3, as shown in FIG. 1. The shown inductance L1 exhibits the inductance component of the loop antenna 2, and the resistance R1 exhibits the resistance component of the loop antenna 2. The loop antenna 2 may be expressed by an equivalent circuit including the inductance L1 and resistance R1, which are connected in series.
In a receiving operation, the loop antenna 2 receives a modulated wave (signal) transmitted from a reader/writer (not shown) and supplies the received modulated wave to the transmitting/receiving circuit 3. The transmitting/receiving circuit 3 then performs predetermined processing on the modulated wave supplied from the loop antenna 2 and supplies the resulting receive data to a CPU (Central Processing Unit) (not shown). In a transmitting operation, the transmitting/receiving circuit 3 performs predetermined processing on the send data supplied from the CPU (not shown) and supplies the resulting modulated wave (signal) to the loop antenna 2. The loop antenna 2 transmits the modulated wave from the transmitting/receiving circuit 3 to the reader/writer (not shown).
In the front end circuit 1 in FIG. 1, the capacitor Cl is connected in parallel across the serially connected resistance R1 and inductance L1, which is defined to resonate at a predetermined frequency. In other words, the front end circuit 1 operating in the card mode includes a parallel resonant circuit resulting from the connection of the capacitor C1 to the loop antenna 2 in parallel, as shown in FIG. 1, such that the front end circuit 1 can communicate with the reader/writer (not shown) efficiently.
The front end circuit 1 of a non-contact type IC card in the past, which operates in the reader/writer mode, includes a capacitor C2, the loop antenna 2, a receiving circuit 4 and a transmitting circuit 5, as shown in FIG. 2. The same reference numerals are given to the same components as those in FIG. 1, and the description will be omitted (appropriately) herein.
In a receiving operation, the loop antenna 2 receives a modulated wave (signal) transmitted from an IC card (not shown) and supplies the received modulated wave to the receiving circuit 4. The receiving circuit 4 then performs predetermined processing on the modulated wave supplied from the loop antenna 2 and supplies the resulting received data to a CPU (not shown). In a transmitting operation, the transmitting circuit 5 performs predetermined processing on the send data supplied from the CPU (not shown) and supplies the resulting modulated wave (signal) to the loop antenna 2. The loop antenna 2 then transmits the modulated wave supplied from the transmitting circuit 5 to the IC card (not shown).
In the front end circuit 1 in FIG. 2, the capacitor C1, resistance R1 and inductance L1 are serially connected, resulting in a resonant circuit. In other words, the front end circuit 1 operating in the reader/writer mode includes a serial resonant circuit in which the capacitor C2 and loop antenna 2 are connected in series, as shown in FIG. 2, which allows efficient communication with another non-contact type IC card (not shown).
As described above, the front end circuit 1 in the past has different circuit constructions one of which is optimum for the operation in the card mode and the other of which is optimum for the operation in the reader/writer mode. In general, the loop antenna 2 in the card mode has a better communication characteristic (receiving characteristic) with more turns while the loop antenna 2 in the reader/writer mode has a better communication characteristic (transmitting characteristic) with fewer turns.
Notably, the better communication characteristic of the loop antenna 2 in the reader/writer mode with fewer turns is limited to the case with the transmitting circuit 5 being capable of energizing by constant voltage driving.
Furthermore, there is provided (as disclosed in JP-A-2003-36427 (Patent Document 1)) a semiconductor integrated circuit apparatus, which operates in either card mode or reader/writer mode for external equipment, driving an antenna that communicates with the equipment by using a differential output based on a send data signal and send carrier signal to be transmitted to the equipment, and detecting data transmitted from the equipment based on the signal supplied from the antenna and rectified in a parasitic diode bridge circuit.